i want to add a loop so that it works like this.

ti = 0;
tf = 1E-3;
tspan=[ti tf];
KC = 4E-3;
y0= [ (10e-6)*rand(2,1); ((-3.14).*rand(1,1) + (3.14).*rand(1,1));
      (10e-6)*rand(2,1); ((-3.14).*rand(1,1) + (3.14).*rand(1,1));
      (10e-6)*rand(2,1); ((-3.14).*rand(1,1) + (3.14).*rand(1,1)); 
      (10e-6)*rand(2,1); ((-3.14).*rand(1,1) + (3.14).*rand(1,1)); 
      (10e-6)*rand(2,1); ((-3.14).*rand(1,1) + (3.14).*rand(1,1));
      ((-3.14).*rand(5,1) + (3.14).*rand(5,1))];
yita_mn = [
    0 1 0 0 1;
    1 0 1 0 0; 
    0 1 0 1 0;
    0 0 1 0 1;
    1 0 0 1 0;
      ]*(KC);
N = 5;
t = 1E-3;
[T,Y]= ode45(@(t,y) rate_eq(t,y,yita_mn,N),tspan,y0);

figure(1)
plot(T./t,(Y(:,16)),'linewidth',0.8);
hold on 
for m = 16:20
    plot(T./t,(Y(:,m)),'linewidth',0.8);
end 
hold off
grid on
xlabel("time")
ylabel("phase difference")
set(gca,'fontname','times New Roman','fontsize',18,'linewidth',1.8);


function dy = rate_eq(t,y,yita_mn,N,o)

dy = zeros(4*N,1);
dGdt = zeros(N,1);
dAdt = zeros(N,1);
dOdt = zeros(N,1);
P = 0.05;
a = 5;
T = 2E3;
Gt = y(1:3:3*N-2);
At = y(2:3:3*N-1);
Ot = y(3:3:3*N-0);
k = 4E-3;
for i = 1:N
    dGdt(i) = (P - Gt(i) - (1 + 2.*Gt(i)).*(At(i))^2)./T ; 
    dAdt(i) = (Gt(i).*(At(i)));
    dOdt(i) = -a.*(Gt(i));  
    for j = 1:N
        dAdt(i) = dAdt(i)+yita_mn(i,j).*(At(j))*sin(Ot(j)-Ot(i));
        dOdt(i) = dOdt(i)+yita_mn(i,j).*((At(j)/At(i)))*cos(Ot(j)-Ot(i));
    end
n1 = (1:5)';
n2 = circshift(n1,-1);
n16 = n1 + 15;
n17 = circshift(n16,-1);
n20 = circshift(n16,1);

j2 =  3*(1:5)-1;
j5 = circshift(j2,-1);
j8 = circshift(j2,-2);
j19 = circshift(j2,1);

%%%%%%%%%%%%%%%%%%%%%%%%%%% here i wanted to add a loop so that when
% Gt(i) = Gt(1) then the Gt(i+1) = 2 and when the Gt(i) = Gt(5) then the Gt(i+1) = Gt(1)
%i dont know how to addd this loop pelase help me in it.

dy(n16) =  -a.*(Gt(i+1) -Gt(i)) - (k).*(y(j2)./y(j5)).*sin(y(n16)) - (k).*(y( j5)./y(j2)).*sin(y(n16)) + (k).*(y(j8)./y(j5)).*sin(y(n17)) + (k).*(y(j19)./y(j2)).*sin(y(n20));  

end

dy(1:3:3*N-2) = dGdt;
dy(2:3:3*N-1) = dAdt;
dy(3:3:3*N-0) = dOdt;

end

Answer 1

[Jeffrey Clark]

@SAHIL SAHOO, since Gt(1) is not changed after the initial setting from the y input, and Gt(i+1) is not refereced before where you say you want to change Gt(i+1), you can just set Gt(2:end) before the i loop:

Gt = y(1:3:3*N-2);
% Gt(i) = Gt(1) then the Gt(i+1) = 2 and when the Gt(i) = Gt(5) then the Gt(i+1) = Gt(1)
Gt([false Gt(1:end-1)==Gt(1)]) = 2;
Gt([false Gt(1:end-1)==Gt(5)]) = Gt(1);

[SAHIL SAHOO]

can you please help me how to add this in my code, please if you can edit that will be very helpful.

[Jeffrey Clark]

@SAHIL SAHOO, you askeda very specific question which is what I answered and showed the two lines added just after where Gt is defined. I suspect you are asking the more general question as to why you aren't getting the results you want? Please check that the code you pasted in your initial post is what you are running, when I reformatted it slightly and without adding my two lines the code debugger points out that the parameters for the call to rate_eq don't match the functions', and the function doesn't use its first or last parameter t and o (see attached your reformatted code). It is also unlikely that Gt(i) would ever be exactly the same as Gt(1) or Gt(5) since they are random numbers:

[T,Y]= ode45(@(t,y) rate_eq(t,y,yita_mn,N),tspan,y0);

function dy = rate_eq(t,y,yita_mn,N,o)

[SAHIL SAHOO]

i get coreect solution by using the n